(1) Field of the Invention
The present invention relates to a semiconductor device incorporating a memory cell array, for example, a random-access memory (RAM), more particularly to a semiconductor device incorporating a test pattern generating circuit able to test the internal state of the memory cell array before shipment of the semiconductor device.
(2) Description of the Related Art
Generally, in a semiconductor device incorporating a memory cell array (for example, RAM) various kinds of logic circuits are provided in addition to the memory cell array for transmitting or receiving signals to or from the array.
Such logic circuits include, for example, counter circuits and arithmetic logic units (ALU). Address signals for the memory cell array are supplied from the output side of the counter circuits, and data which has been calculated in the ALU's is supplied from the output side of ALU's to the array and written into the predetermined address. Also, predetermined data read from the memory cell array is supplied to the input side of the ALU's in order, for example, to carry out predetermined calculation in the ALU's again.
In the prior art, if it was desired to test the function or the internal state of the memory cell array, the test was carried out through the above logic circuits. However, in this case, the test data to be written into the memory cell array was designated from the outside. Therefore, there was the problem that it was necessary to use a large amount of test data, resulting in poor efficiency for the testing.
In view of the above, it has been desired to provide a test circuit, within the above semiconductor device, enabling direct testing without the need for supplying test data from the outside.
However, even if such a test circuit is used, there is a problem that the test pattern constituting the test data to be written into each memory cell becomes large, especially when the capacity of the memory cell array is large. As a result, the writing of the test data for the memory cell array is still troublesome.